Reaction Mechanism Principles
Bond polarity, homolytic and heterolytic fission, radicals, electrophiles, nucleophiles, curly-arrow conventions and comparing addition, substitution, elimination and condensation.
How to study A-level Chemistry
Represent the species and process correctly, conserve atoms, charge and energy, calculate with units, then test the result against observations and chemical evidence.
Core concepts
Concept 1
Mechanisms model electron movement and bond changes using defined species and arrow conventions.
Exam cue: Start each full curly arrow at an electron pair or covalent bond.
Concept 2
Bond polarity and electron density help predict electrophilic or nucleophilic attack, while stability and conditions influence pathways.
Exam cue: Show intermediates with correct charges and all relevant lone pairs.
Concept 3
A mechanism must conserve atoms and charge and produce the stated overall reaction when its steps are combined.
Exam cue: Check that the regenerated catalyst and eliminated small species are present where required.
Risk pitfalls and guardrails
Using curly arrows to show atom movement rather than electron-pair movement.
Guardrail: Do not substitute a memorised equation, mechanism or trend until you have identified the species, conditions and chemical model required.
Changing a species' charge without showing the bond-breaking or bond-forming step.
Guardrail: Do not substitute a memorised equation, mechanism or trend until you have identified the species, conditions and chemical model required.
Memorising a mechanism without checking reagent and conditions.
Guardrail: Do not substitute a memorised equation, mechanism or trend until you have identified the species, conditions and chemical model required.
Memory anchors
Heterolytic Fission
Both bonding electrons go to one atom, forming ions.
Curly Arrow
A full curly arrow shows movement of an electron pair.
Electrophile
An electrophile accepts an electron pair to form a bond.
Nucleophile
A nucleophile donates an electron pair to form a bond.
Intermediate
An intermediate forms in one elementary step and is consumed in a later step.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
What does a full curly arrow represent in an organic mechanism?
What does a single-headed fishhook arrow represent?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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